Positron-emission tomography (PET) is a nuclear medicine functional imaging technique that is used to analyze metabolic processes in the body in order to diagnose the disease. PET is utilized as both a medical and research tool. In medicine, it is used in clinical oncology and diagnosis of certain diffuse brain diseases. As a research tool, PET is used to map the heart function and normal human brain, and also support drug development. Single-photon emission computed tomography (SPECT) is a nuclear medicine tomographic imaging technique. It primarily uses gamma rays. It delivers a gamma-emitting radioisotope into the patient via injection into the bloodstream. SPECT is used to complete any gamma imaging study such as bone scintigraphy, infection imaging, thyroid imaging and tumor imaging. It is also used to provide information about the localized function in internal organs, such as functional cardiac and brain imaging. This book provides comprehensive insights into the field of PET and SPECT Imaging. It traces the progress of these fields and highlights some of its key concepts and applications. This book will serve as a valuable source of reference for graduate and post- graduate students.